Nylon is a series of polymers having the general formula —[(CH2)n—CONH]— or —[(CH2)n—CONH—(CH2)m—NHCO]—, typically named with the length of the methylene units separating the amide functions. Some examples are nylon 6, nylon 7, nylon 8, nylon 9, nylon 11, nylon 12, and nylon 13.
Nylon 11 and nylon 12 in particular possess excellent chemical resistance, thermal resistance, cold impact resistance, flexibility, and durability. There are many industrial applications of these nylons, including automotive, sports, medical, high-performance cables, electronics, electrical materials, and even lenses for glasses. Currently, about 100,000 metric tons of nylon 11 and nylon 12 are produced annually. The use of these nylons in the automotive/transportation industry is increasing at an annual rate of 33.7%, extrapolated to 250,000 metric tons by 2016. Similarly, their use in photovoltaic panels is expected to increase at an annual rate of 36.1% through 2016, and in other general applications is predicted to increase at 25.3% annually through 2016. Nylon 13 has analogous characteristics to nylon 12 and may be used in similar applications as nylon 12.
Nylon 11, 12, and 13 can be produced from amino acids or their derivatives such as esters or lactams (cyclic amide of the amino acid). Currently, the main supply source of C12 amino acid (in lactam form) is from Evonik Industries, of Essen, Germany, which produces this precursor of nylon 12 from petroleum-derived butadiene in a six-step process. While the carbon backbone can be obtained from petrochemical sources by chemical synthesis, there is an increasing interest in the use of renewable resources for production of these amino acids (and their derivatives), due to growing environmental and sustainability concerns. As such, approaches that use natural fatty acids and esters from plant- or algae-derived biomass as the starting materials are attractive. Among the natural fatty acids, oleic acid is the predominant component of lipids in most vegetable oils (e.g., soy oil) and algae.
Conventional approaches to produce 11-aminoundecanoic acid (C11 amino acid) from oleic acid or recinoleic acid (the main component of castor oil)—involve subjecting the acid or ester to a cross metathesis reaction with acrylonitrile to produce 10-cyano-9-decenoic acid or ester, followed by reduction using high-pressure hydrogenation to remove unsaturation. (PRIOR ART FIG. 1, top reaction.) 12-Aminododecanoic acid (C12 amino acid) is also prepared in analogous fashion starting from 10-undecenoic acid prepared from pyrolysis of recinoleic acid. (PRIOR ART FIG. 1, bottom reaction.) It has been stated that α-ω-diacids or diesters can be synthesized by homometathesis or fermentation, or acids or esters with a terminal olefin can be prepared from ethylenolysis as the starting material in lieu of oleic acid. In one method, 10-undecenitrile derived from 10-undecylenic acid derivatives, readily available from recinoleic acid, is subjected to cross metathesis with methyl acrylate, delivering a similar cyano-ester which upon hydrogenation provides C12 amino-esters. 10-Undecenitrile is also subjected to tandem isomerization/hydroformylation and oxidation to access an analogous cyano acid, which can be converted to C12 amino acid.
Finally, another method starts with either 9-decenoic or 10-undecenoic acids or esters (or other ω-terminal fatty acids with various chain lengths) that are subjected to cross-metathesis with either 2-pentenenitrile or 3-pentenenitrile, resulting in unsaturated nitriles or their esters. (PRIOR ART FIG. 2.) This method produces unsaturated nitriles and esters that are then hydrogenated using known methods. Notably, this method produces low yields (between 13-30%) when 3-pentenenitrile is used to produce nylon 12 amino acid. Alternatively, 10-undecenoic acid can be hydrocyanated and then hydrogenated for C12 amino acid production.
There is a need for additional and improved renewable methods of producing nylons, and their precursors, that are simpler, cheaper, and/or involve milder reaction conditions.